The field of the invention is electronic transmission control systems for automotive vehicles, and more specifically, devices which adjust the operating parameters of electronic transmission control systems.
Generally, an electronic transmission for an automotive vehicle such as a passenger car or small truck comprises a gear mechanism and an electronic control system. The gear mechanism is constructed to provide, in response to electrical signals received from the electronic control system, a plurality of rotational speed ratios between a power input shaft and a power output shaft. The precise rotational speed ratio provided by the gear mechanism is determined by selectively coupling various pairs of friction engaging mechanisms comprised within the gear mechanism, such as hydraulically activated clutches. To apply hydraulic fluid pressure to a particular pair of friction engaging mechanisms the electronic control system activates an electronic switching valve associated with each friction engaging mechanism. The electronic switching valves in turn cause pressure from a hydraulic pressure source (internal line hydraulic fluid pressure) to be applied to the friction engaging mechanisms, thus causing the components of such mechanisms to be pressed together in a fluid medium. As the components move toward each other in the fluid medium, friction results between them, thus causing them to communicate and eventually to couple.
It follows that to maximize efficiency during gear shifts and to minimize deterioration of the friction engaging mechanisms during operation, electronic control systems are advantageous for regulation of the coupling of friction engaging mechanisms. This is also true for maximizing drivability. For example, if the friction engaging mechanisms couple too quickly (if too much hydraulic fluid pressure is applied to the friction engaging mechanisms), gear shifting will occur in a jerky fashion and the shock resulting from the coupling can be unpleasant and in extreme cases could result in damage to the transmission as well as to other components of the vehicle drive train. On the other hand, if the coupling takes place too slowly (if insufficient hydraulic fluid pressure is applied to the friction engaging mechanisms), excessive slip and, therefore, wear may occur between the friction engaging mechanisms.
To insure smooth shifting and efficient coupling of the friction engaging mechanisms, conventional electronic transmissions utilize an electronic pressure valve to adjust the internal line hydraulic fluid pressure of the gear mechanism. Typically, the electronic pressure valve adjusts the internal line hydraulic fluid pressure in proportion to an electrical current emitted by the electronic control system. The amount of emitted current, and hence the internal line hydraulic fluid pressure, is generally determined by the electronic control system based on a number of factors which indicate the load placed on an engine associated with the transmission. These factors often include the throttle or accelerator output, the acceleration of the vehicle, the amount of torque desired between the friction engaging mechanisms, and the timing of any gear shifts.
The changes in the internal line hydraulic fluid pressure produced by these factors may be summarized as follows. When the engine associated with the transmission operates at idle output, the electronic control system sets the internal line hydraulic fluid pressure at a very low level; and the frictional communication between the friction engaging mechanisms is minimized. As the output of the engine increases, the electronic control system raises the internal line hydraulic fluid pressure, the frictional communication between the friction engaging mechanisms increases, and eventually sufficient torque is applied to the transmission output shaft to cause the shaft to rotate and the vehicle to accelerate. As the vehicle accelerates, the difference between the rotational speeds of the friction engaging mechanisms decreases, and the hydraulic pressure required to hold the friction engaging mechanism together is reduced. It should be noted that during gear shifts similar changes in the internal line hydraulic fluid pressure are desired because a new pair of friction engaging mechanisms must be brought together.
Because most conventional electronic control systems control internal line hydraulic fluid pressure based at least in part on engine load interpreted as a function of throttle output and acceleration, modifying the power output of an engine may result in regulation of the internal line hydraulic fluid pressure based on incorrect load assumptions. When a performance enhancement device is added to an engine, the power generated by the engine increases, and the throttle position required to carry a given load is reduced. Consequently, the electronic control system may incorrectly perceive that the engine is carrying a reduced load. In response to the perceived load reduction, the electronic control system may reduce the internal line hydraulic fluid pressure of the transmission where the load actually was not reduced. Such systems also do not adequately account for situations where firmer shifting is desireable even with unmodified engine power, such as when pulling a trailer.